Technical Field
The present disclosure relates to illumination, and more particularly to efficient power control for illumination systems.
Description of the Related Art
Luminaires enjoy widespread use in a variety of industrial, commercial, and municipal applications. Such applications can include general or area lighting of workspaces, roadways, parking lots, and the like. Multiple luminaires are typically arranged in patterns and positioned at intervals sufficient to provide a minimum overall level of illumination across the area of interest. For example, luminaires may be spaced at intervals along a driveway in a multilevel parking garage to provide an overall level of illumination that permits safe ingress and egress by pedestrians as well as permits safe operation of motor vehicles within the parking garage. In a similar manner, luminaires may be spaced at intervals throughout a commercial center parking lot to promote safe operation of motor vehicles, permit safe ingress and egress by customers, and foster a sense of safety and well-being for business patrons within the commercial center. Similarly, a number of luminaires may be spaced along a roadway to provide a level of illumination permitting safe operation of motor vehicles on the roadway and, where applicable, safe passage of pedestrians on sidewalks adjoining the roadway.
Energy conservation has become of ever-increasing importance. Efficient use of energy can result in a variety of benefits, including financial benefits such as cost savings and environmental benefits such as preservation of natural resources and reduction in “green house” (e.g., CO2) gas emissions.
Residential, commercial, and street lighting which illuminate interior and exterior spaces consume a significant amount of energy. Conventional lighting devices or luminaires exist in a broad range of designs, suitable for various uses. Lighting devices employ a variety of conventional light sources, for example incandescent lamps, fluorescent lamps such as high-intensity discharge (HID) lamps (e.g., mercury vapor lamps, high-pressure sodium lamps, metal halide lamps).
One approach to reducing energy consumption associated with lighting systems employs higher efficiency light sources. Use of higher efficiency light sources may, for instance, include replacing incandescent lamps with fluorescent lamps or even with solid-state light sources (e.g., light emitting diodes (LEDs), organic LEDs (OLEDs), polymer LEDs (PLEDs)) to increase energy efficiency.
Solid-state light sources require a power converter to operate off of alternating current (AC) lines, also referred to as AC mains. The converter is typically a switch mode converter topology, such as flyback converter, LLC resonant converter, or the like. Other power converters that may be used are of the “AC LED” type, which switch in, or out, a variable number of solid-state light sources so that the forward voltage drop is close to the rectified AC line voltage.
Solid-state light sources are best powered using a constant current. This is due to the constant forward voltage (Vf) of the solid-state light source, for example, 3 volts. If a constant voltage converter is used, small variations in Vf of the solid-state light source(s) (e.g., due to temperature) will result in large variations in current through the solid-state light source(s). These large variations in current will cause significant changes in light output and possibly damage the solid-state light source(s) by exceeding its rated power handling capacity.